The metal foil type resistor was introduced as a high reliability resistor long after the wire-wound cylindrical type resistors and metal thin film cylindrical type resistors had won such recognition. The metal foil type resistor inherently has an advantage over a wire-wound resistor in that there is no inductance problem and an advantage over a thin film cylindrical resistor in that the sheet of foil is a relatively thick uniform material whose PPM resistance value is known and whose TCR value is known and which values can be relied upon. The metal foil type resistor was from its inception designed to have the metal foil sheet secured to one side (normally embedded in a layer of epoxy resin) of a substrate which had two flat sides. It was deemed important in the design of the metal foil type resistor that both sides of the substrate be formed flat and that both sides have the same thickness of epoxy resin applied thereto so that the stresses, created by the difference in the linear coefficient of expansion between the substrate and the metal foil layer, are offset by the equal mechanical constraint of the epoxy resin layers. This principle is described in the U.S. Pat. No. 3,405,381 to F. Zandman et al.
It has been found that if the substrate is selected to have a lower linear expansion coefficient than the metal foil, (in particular, if the difference in the linear coefficient of expansion between the metal and the insulating base is selected to be 26 to 66 .times. 10.sup.-7 /.degree. C), then the metal foil resistor can be fabricated with a molded assembly with little regard as to whether or not the epoxy resin layers on either of the substrate are of equal depth. This improvement is described in U.S. Pat. No. 3,824,521 to Horii et al. The present invention improves the TCR characteristics of the metal foil type resistor even further than the improvement just described.